A selective call communication system comprises a transmitter and a number of receivers. Each receiver is adapted to intercept the same carrier wave frequency, but is responsive to a predetermined tone or set of tones. Present systems on the market are two basic types. In one type, the receivers are not capable of reproducing a voice message, but rather produce an audible or visual alerting signal. In such a system, a given receiver will emit an alerting signal when the carrier wave is modulated with the tone or tones associated with that receiver. The possessor of such a receiver will then perform some previously agreed upon action such as calling his office. Different tones or sets of tones modulated on that carrier wave will activate other receivers. The other type of system enables voice communication. The audio circuitry in each receiver is squelched until the associated tone or set of tones is received. Then, the receiver becomes unsquelched to reproduce the ensuing voice message.
The advantage of a system in which the selected receiver emits an alerting signal is that many communications can occur in a given time period since each communication is essentially momentary. In a system which contemplates voice communication, much more "air time" is consumed in transmitting such messages. However, a system in which the receivers emit only alerting signals suffers the disadvantage of not being capable of voice communication in certain instances when that is necessary.
A further disadvantage of presently available systems in which the receivers furnish an alerting signal is that only one piece of information can thereby be conveyed. In other words, only a single previously agreed-upon action can be taken by the bearer of the receiver when he perceives an alerting signal.
Some presently available selective call communication systems have what is commonly referred to as a "group-call" feature, which enables simultaneous communication with a group of receivers. It has also been proposed that each receiver be a member of more than one group, for example, a member of a group of 10 and a member of a group of 100. Then, depending upon the situation, a signal can be sent to all receivers in the group of 10, or to all receivers in the group of 100. However, such proposals do not call for means to apprise the bearer of such receiver whether a group is receiving the page, and which group is receiving the page.